1. Field of the Invention
The present invention relates to a technique for detecting voltage values of a plurality of power storage elements and discharging power storage elements to suppress variation of the voltage values in a plurality of power storage elements.
2. Description of Related Art
Japanese Patent Application Publication No. 2001-218376 (JP 2001-218376 A) describes a technique for detecting voltage values of a plurality of cells connected in series and discharging a specific cell such that variation of the voltage values in a plurality of cells falls within an allowable range. In each of the cells, a discharge resistor and a discharge switch are connected in parallel, and a specific discharge switch is turned on, thereby discharging only the specific cell.
As in JP 2001-218376 A, if variation of the voltage values in a plurality of cells is within the allowable range, the abnormal state according to voltage fluctuation can be easily specified by monitoring voltage fluctuation thereafter. If a specific abnormal state is generated, there is a case where voltage fluctuation due to the abnormal state is generated. Therefore, it is possible to determine the generation of the abnormal state by recognizing voltage fluctuation due to the abnormal state. When variation of the voltage values is generated, it is difficult to recognize voltage fluctuation due to an abnormal state. Therefore, it is preferable that variation of the voltage values is within the allowable range.
In JP 2001-218376 A, all cells constituting an assembled battery are connected to one voltage detection circuit. The number of cells constituting the assembled battery is able to be appropriately determined. For example, if the number of cells increases, there is a case where a plurality of voltage detection circuits should be connected to the assembled battery. The detection result of each of the voltage detection circuits optionally includes a detection error, and the detection error is optionally different among the voltage detection circuits. Accordingly, there is a case where variation of the voltage values of the cells in the assembled battery is generated by variation in the detection error of a plurality of voltage detection circuits.
If the cells are discharged such that variation of the voltage values associated with variation in the detection error falls within the allowable range, the time until variation of the voltage values falls within the allowable range is delayed by the discharge time. Accordingly, the determination of the abnormal state described above is delayed.
For example, there is a case where, in order to improve the output of an assembled battery, a plurality of battery stacks are connected in series to constitute the assembled battery. Each battery stack is constituted by connecting a plurality of cells in series. Each battery stack is replaced individually or a plurality of battery stacks are used in different temperature environments, and thus, in the plurality of battery stacks, variation in the full charging capacity of the cells is generated. Accordingly, in the plurality of battery stacks, variation of the voltage values of the cells is likely to be generated.
If the cells are discharged such that variation of the voltage values falls within the allowable range, the time until variation of the voltage values falls within the allowable range is delayed by the discharge time. Accordingly, the determination of the abnormal state described above is delayed.